The present invention relates to shock absorbers for use in automotive vehicles and more particularly to vibration dampers of the type which are mounted upon the shock absorber and are electromagnetically actuated to damp vibrations.
Such shock absorbers are traditionally constructed by having a damping piston which is fastened to a piston rod which divides the work cylinder into two chamber halves filled with a hydraulic damping fluid. The piston typically incorporates valves for restricting the flow of fluid therethrough as the piston moves along the cylinder. The valves are designed to provide a greater resistance in one direction of the piston movement than the other. These valves are usually preset during manufacture and the setting of these valves is not suitable for all vehicle load conditions generated by surfaces over which the vehicle may be driven and/or the speeds at which the vehicle may be driven.
To accommodate varying loads, road surfaces, driving conditions and the like, shock absorbers have been produced with adjustable piston valves and/or with additional controlled valves as a part thereof. These valves for the most part have been adjustable externally of the shock absorber either manually or electromechanically. In some instances, electromagnetically operated damping valves have been included to accommodate this additional adjustable feature. Typical of such, prior art adjustable hydraulic vibration dampers included within shock absorbers are the devices disclosed in U.S. Pat. Nos. 4,638,896; 5,559,700; 5,409,089; 4,723,640; 4,785,920; 4,854,429.